Abstract Information :

Ion mobility mass spectrometry is a separation technique that hyphenates to mass spectrometry and can separate, assist in assignment, and reveal properties of ions on a complementary timescale. Ions are separated based on their differential mobility based on factors including size, shape and charge distribution. Ion mobility has proven useful as a tool to separate components in complex mixtures and to differentiate ions where mass spectrometry alone proved challenging, and a deeper understanding of physicochemical properties that affect ion mobility is developing. From ion mobility drift-times collision cross-sections can either be calculated or derived based on calibration routines. Measuring collision cross-sections and recorded them in commercial and public databases is becoming commonplace with vendor offerings, public online databases and publications. Predicting collision cross-sections using molecular modelling and/or chemometrics can identify components that are not recorded in databases. .

Exciting developments in ion mobility include increasing complementarity of molecular modelling approaches focussed on modelling ensembles of molecular geometries and charge distributions with closer approximations to the true state of ions in the gas-phase under different ion mobility regimes e.g. linear vs. non-linear fields. Orthogonal activation and interrogative techniques such as UV photodissociation enable understanding of corresponding relative stabilities and collection of spectroscopic data useful to refine singular assignments and wider global prediction models.

The flexibility of ion mobility has allowed researchers to develop, and users to capitalise on, a variety of different ion mobility separation techniques but crucially the differences in their performance is a challenge to grapple with, and to understand the limitations and advantages. A combination of ion mobility, mass spectrometry, molecular modelling and orthogonal measurements offers an unprecedented opportunity to collect data on gas-phase ions and utilise these data to separate, and assign structures to, ions.